A piezoelectric sensing device is described for measuring material thickness of targets such as pipes, tubes, and other conduits that carry fluids. The piezoelectric sensing device includes a piezoelectric element mounted to a flexible circuit with glass reinforced polyimide C-stage cover layers surrounding a pure polyimide C-stage core.

Claim:

What is claimed is:

1. A piezoelectric sensing device comprising: a plurality of piezoelectric elements; and a flexible circuit comprising a pure polyimide C-stage core between a first copperlayer on a first side of the pure polyimide C-stage core and a second copper layer on a second side pure polyimide C-stage core opposite the first side, a first glass reinforced polyimide C-stage cover layer formed over the first copper layer, and asecond glass reinforced polyimide C-stage cover layer formed over the second copper layer, wherein the plurality of piezoelectric elements are mounted to the flexible circuit in a plurality of windows formed in the first glass reinforced polyimideC-stage cover layer to receive the plurality of piezoelectric elements.

8. The piezoelectric sensing device of claim 7, wherein the plurality of piezoelectric elements are soldered to the ground electrodes and the hot electrodes.

9. The piezoelectric sensing device of claim 3, further comprising a plurality of plated vias extending through the pure polyimide C-stage core to connect one or more of the first plurality of conductors to one or more of the second pluralityof conductors.

10. The piezoelectric sensing device of claim 3, further comprising a connector on a first end of the flexible circuit, wherein the connector is coupled to the first plurality of conductors and the second plurality of conductors.

12. A piezoelectric sensing device comprising: a plurality of ceramic piezoelectric transducers; and a flexible circuit comprising a pure polyimide C-stage core between a first plurality of conductors on a first side of the pure polyimideC-stage core and a second plurality of conductors on a second side pure polyimide C-stage core opposite the first side, a first glass reinforced polyimide C-stage cover layer formed over the first plurality of conductors, and a second glass reinforcedpolyimide C-stage cover layer formed over the second plurality of conductors, wherein the plurality of piezoelectric elements are mounted to the flexible circuit in a plurality of windows formed in the first glass reinforced polyimide C-stage cover layerto receive the plurality of ceramic piezoelectric transducers, and wherein the windows expose ground electrodes and hot electrodes to which the plurality of ceramic piezoelectric transducers are soldered.

13. The piezoelectric sensing device of claim 12, further comprising a first plating layer on the first plurality of conductors.

15. The piezoelectric sensing device of claim 13, wherein the first plating layer is applied only on the portion of the first plurality of conductors exposed by the plurality of windows.

16. The piezoelectric sensing device of claim 12, further comprising a plurality of plated vias extending through the pure polyimide C-stage core to connect one or more of the first plurality of conductors to one or more of the second pluralityof conductors.

17. The piezoelectric sensing device of claim 12, further comprising a connector on a first end of the flexible circuit, wherein the connector is coupled to the first plurality of conductors and the second plurality of conductors.

The subject matter disclosed herein relates to measuring material thickness using ultrasonic transducers and in one embodiment to a piezoelectric sensing device that comprises a flexible circuit for use in high temperature environments.

Several industries (e.g., oil and gas, refinery, chemical, power generation) require the transport of fluid (e.g., liquids or gases) through pipes. Nondestructive testing systems can be placed on the outer surface of these pipes to monitorcorrosion/erosion of the pipes, including corrosion/erosion on the interior of pipe walls. These systems are usually implemented as part of manual inspection over the course of time, wherein the pipe wall thickness and changes in the thickness aremonitored over time. In some cases, the probe or other nondestructive testing device is permanently coupled to the outer surface of the pipe to continuously monitor corrosion/erosion at that location to determine pipe corrosion/erosion rates and todetermine whether that pipe location is in need of preventative maintenance to prevent a pipe failure.

One example of a nondestructive testing system used to monitor corrosion/erosion of a pipe is an ultrasonic testing system. When conducting ultrasonic testing of a pipe, an ultrasonic pulse is emitted from a probe coupled to the outer surfaceof the pipe and passed through the pipe wall. As the ultrasonic pulse passes into and through the pipe wall, various pulse reflections called echoes are reflected back to the probe as the pulse interacts with the outer surface of the pipe, internalstructures within the pipe wall, and with the back wall of the pipe wall. The echo signals can be displayed on a screen with echo amplitudes appearing as vertical traces and time of flight or distance as horizontal traces. By tracking the timedifference between the transmission of the ultrasonic pulse and the receipt of the echoes, various characteristics of the pipe can be determined, including pipe wall thickness. If the thickness of the pipe wall at the location of the ultrasonic testingsystem decreases over time (e.g., as would be shown be a reduction in the time of flight of the back wall echo), this can be an indication of corrosion/erosion.

Various factors influence the configuration of devices and in particular the materials for use in these non-destructive testing systems. Operating conditions such as the operating temperature in some applications, for example, can exceed thetemperature thresholds of materials such as copolymers of polyvinylidene fluoride (PVDF) (e.g., P(VDF-TrFE)) or polytetrafluoroethylene (PTFE)). Processing conditions including temperatures related to certain processing steps during manufacture are alsolimiting. Performance factors such as accuracy and sensitivity to small defects and to small changes in material thickness are other factors that preclude the use of particular materials and combinations thereof. However, while improved performance canbe achieved using certain configurations of materials, these configurations often result in physical characteristics (e.g., height profile) that limit the applicability of the resultant devices in certain applications, including high temperatureapplications (e.g., nuclear power generation environments which are routinely operating well above 120.degree. C.).

The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE INVENTION

A piezoelectric sensing device is described for measuring material thickness of targets such as pipes, tubes, and other conduits that carry fluids. The piezoelectric sensing device includes a piezoelectric element mounted to a flexible circuitwith glass reinforced polyimide C-stage cover layers surrounding a pure polyimide C-stage core. An advantage that may be realized in the practice of some disclosed embodiments of the piezoelectric sensing device is that the device can be used in hightemperature applications above 120.degree. C. and, in some cases, as high as 300.degree. C.

In one embodiment, a piezoelectric sensing device is disclosed. The piezoelectric sensing device comprises a plurality of piezoelectric elements, and a flexible circuit comprising a pure polyimide C-stage core between a first copper layer on afirst side of the pure polyimide C-stage core and a second copper layer on a second side pure polyimide C-stage core opposite the first side, a first glass reinforced polyimide C-stage cover layer formed over the first copper layer, and a second glassreinforced polyimide C-stage cover layer formed over the second copper layer, wherein the plurality of piezoelectric elements are mounted to the flexible circuit in a plurality of windows formed in the first glass reinforced polyimide C-stage cover layerto receive the plurality of piezoelectric elements.

In another embodiment, the piezoelectric sensing device comprise a plurality of ceramic piezoelectric transducers, and a flexible circuit comprising a pure polyimide C-stage core between a first plurality of conductors on a first side of thepure polyimide C-stage core and a second plurality of conductors on a second side pure polyimide C-stage core opposite the first side, a first glass reinforced polyimide C-stage cover layer formed over the first plurality of conductors, and a secondglass reinforced polyimide C-stage cover layer formed over the second plurality of conductors, wherein the plurality of piezoelectric elements are mounted to the flexible circuit in a plurality of windows formed in the first glass reinforced polyimideC-stage cover layer to receive the plurality of ceramic piezoelectric transducers, and wherein the windows expose ground electrodes and hot electrodes to which the plurality of ceramic piezoelectric transducers are soldered.

This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define orlimit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is notlimited to implementations that solve any or all disadvantages noted in the background.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted,however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are notnecessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understandingof the invention, reference can be made to the following detailed description, read in connection with the drawings in which:

FIG. 1 is a schematic diagram of an exemplary embodiment of a measurement system;

FIG. 2 is an exploded assembly view of an exemplary embodiment of a piezoelectric sensing device;

FIG. 3 is a side, cross-section, assembled view of the piezoelectric sensing device of FIG. 2;

FIG. 4 is a front view of another exemplary embodiment of a piezoelectric sensing device;

FIG. 5 is a side, cross-section view of the piezoelectric sensing device of FIG. 4;

FIG. 6 is a front view of yet another exemplary embodiment of a piezoelectric sensing device;

FIG. 7 is a side, cross-section view of the piezoelectric sensing device of FIG. 6;

FIG. 8 is a front view of still another exemplary embodiment of a piezoelectric sensing device;

FIG. 9 is a side, cross-section view of the piezoelectric sensing device of FIG. 8;

FIG. 10 is a schematic diagram of an implementation of a piezoelectric sensing device such as the piezoelectric sensing devices of FIGS. 2-5; and

FIG. 11 is a schematic diagram of another implementation of a piezoelectric sensing device such as the piezoelectric sensing devices of FIGS. 2, 3, and 6-9.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, there is illustrated in FIG. 1 an exemplary embodiment of a measurement system 10 with improved sensitivity and construction, the latter of which is beneficial for implementation of the measurement system 10 atoperating temperatures greater than, e.g., 120.degree. C., and in areas where access by other measurement systems is limited. The measurement system 10 can comprise a transducer array 12 and instrumentation 14, which is operatively coupled to thetransducer array 12 via a connection 16. The transducer array 12 can comprise one or more sensing elements 18, each of the sensing elements 18 having a piezoelectric element 20 coupled to a substrate 22.

Transducer array 12 can be disposed on a target, such as a pipe, a tube, and related conduits that can be subject to corrosion and erosion by way of the fluid that is transported therein. The disposition of the transducer array 12 permitsultrasonic signals generated by the piezoelectric element 20 to impinge on the material of the target. These ultrasonic signals are reflected such as by surfaces of the material, wherein the reflected signals are detected by the piezoelectric element20.

In one embodiment, instrumentation 14 can include an ultrasonic test unit 24 that generates waveform pulses (generally, "inputs"), which are applied to the piezoelectric element 20 via the connection 16. The waveform pulses cause a mechanicalchange (e.g., a dimensional change) in the piezoelectric element 20. This change can cause an acoustic wave, which is transmitted through the material of the target. Conversely, the piezoelectric element 20 generates a voltage difference when acousticwaves reflected from the material under inspection contact the surface of the piezoelectric element 20. This voltage difference is detected as receive signals (generally, "outputs") by the ultrasonic test unit 24 or other signal processing electronics.

The ultrasonic test unit 24 can include various control means, which are useful to determine the amplitude, timing, and transmit sequence of the waveform pulse generated by the piezoelectric element 20. The waveform pulse is generally in thefrequency range of about 5 MHz to about 20 MHz. By tracking the difference between the transmission of the waveform pulse and the receipt of the received signal and measuring the amplitude of the reflected wave, various characteristics of the materialcan be determined. In one example, the thickness of the material of the target, as well as any corresponding changes in the thickness, can be determined using time-of-flight analysis, the subject matter of which will be recognized by those artisanshaving skill in the transducer and related arts.

In one embodiment, the sensing elements 18 are separately arranged and are constructed as individual sensing units. Communication between these individual units and the ultrasonic test unit 24 is facilitated by the connection 16, and in oneconstruction the connection 16 has a plurality of cables (not shown). These cables are coupled to each of the sensing elements 18. Exemplary cables can include coaxial cables and optical fibers, as well as single and plural strands of copper and/orrelated materials that can conduct the inputs and outputs (e.g., the waveform pulses and the received signals) to and from the piezoelectric element 20 as contemplated herein.

In another embodiment, the sensing elements 18 are arranged on a common substrate, generally demarcated in the present example with the numeral 26. This arrangement is defined by one or more of the piezoelectric elements 20 being disposed onthe common substrate 26. The piezoelectric element 20 of the sensing elements 18 can be spaced apart from one another along for example a strip of material, and as discussed in one or more embodiments below, this material can comprise a flexible circuitmaterial that can conform to the shape of the target. In one example, conductors are incorporated in the flexible circuit material, with each conductor terminating at the piezoelectric element 20 and at the end of the common substrate 26. Theconnection 16 can include one or more connectors (not shown), which are coupled to the conductors, and which can be incorporated or otherwise affixed onto the free end. The connector can be coupled to a mating connector or other device such as a bundleof coaxial cables extending from the ultrasonic test unit 24. This combination can communicate the inputs and outputs between the piezoelectric element 20 and the instrumentation 14.

The number of the sensing elements 18 in the transducer array 12 can vary, and in one construction the number can vary from one to twenty. In one particular example the number is fourteen. An alternative selection of the number can be based onany one or combination of the dimensions of the target under inspection, the preferred spacing of the sensing elements 18 on the target, and the type of defect being detected. When implemented in connection with the common substrate 26, the spacingbetween the approximate centers of the piezoelectric element 20 can be from about 10 mm to about 100 mm. Moreover, in implementations where the sensing elements 18 are arranged as individualized units, each can be located on the target independently ofother ones of the sensing elements 18 of the transducer array 12. Thus the space between adjacent ones of the piezoelectric element 20 and the location of the piezoelectric element 20 relative to features (e.g., edges) of the target can be optimized foreach of the sensing elements 18 as desired.

Although the transducer array 12 is depicted as a linear array (e.g., wherein the sensing elements 18 form a single row with one or more columns) other configurations are also envisioned. In one embodiment, the transducer array 12 can includeone or more rows and one or more columns of sensing elements 18. In another embodiment, the sensing elements 18 are arranged in formations that are different than arrays of rows and columns. By way of example, one formation for transducer array 12 cancomprise a first row of sensing elements 18 and a second row of sensing elements 18, wherein the second row is positioned in perpendicular relation to the first row, thus forming a "t" shape.

Focusing now on the construction of the sensing elements 18, reference can be had to FIGS. 2 and 3. Here there is depicted an exemplary embodiment of a piezoelectric sensing device 100 which can be deployed as one or more of the sensingelements 18 of FIG. 1. In one embodiment, the piezoelectric sensing device 100 can comprise a substrate 102 and a piezoelectric element 104 with a ceramic body 106. The ceramic body 106 can be configured with an electrode 108, a ground 110, and a wraptab 112 constructed of gold plating or comparable conductive material that is deposited on the ceramic body 106. The substrate 102 can comprise a flexible circuit material 114, shown in this example with a first layer 116 and a second layer 118, andwith a receiving area 120 that is configured to receive the piezoelectric element 104. The receiving area 120 can have electrodes 122 for connecting to, e.g., the electrode 108 and the ground 110. The electrodes 122 can include a first or groundelectrode 124 and a second or hot electrode 126. The electrodes 122 can conform to an electrode geometry 128 that is defined by an isolation gap 130 between the electrodes 122 and/or a shape geometry 132 as applied to one or both of the electrodes 122. In one example the shape geometry 132 comprises a t-shaped geometry 134 for the hot electrode 126.

In one embodiment, the piezoelectric sensing device 100 may also include a solder layer 136 that comprises one or more materials such as tin, lead, silver, bismuth, and indium. The solder layer 136 is deposited during assembly and is used tocouple the piezoelectric element 104 to the receiving area 120 of the substrate 102. When assembled, the combination of the substrate 102, the piezoelectric element 104, and the solder layer 136 are arranged as a layered structure 138 with a profileheight P. Embodiments of the piezoelectric sensing device 100 can be configured so that the profile height P does not exceed about 7 mm, and in one example the profile height is from about 0.25 mm to about 1 mm. These values are smaller thanconventional devices, which permits use of the piezoelectric sensing device 100 in places that are generally not accessible with measurement devices of conventional construction.

Materials for use in the ceramic body 106 are selected for their properties including for example compatibility with processing conditions during assembly such as the reflow temperatures required to reflow the solder layer 136. These reflowtemperatures typically are in excess of 200.degree. C. and in one exemplary process the reflow temperatures is about 220.degree. C. Other properties to consider include, but are not limited to, dielectric constant of the material, wherein the materialsthat are selected for the ceramic body 106 should have a dielectric constant that renders good electrical impedance matching, while minimizing the overall dimensions of the piezoelectric element 104. These dimensions include, for example, dimensions forthe rectangular shape of FIG. 2 of about 3 mm by about 5 mm, although the length and width can vary, respectively, from about 2 mm to about 8 mm. In other examples, the shape of the piezoelectric element 104 can comprise a square, a circle, and/or anellipse. With reference to the profile height P discussed above, it is further contemplated that piezoelectric element 104 is formed with an overall thickness from about 0.1 mm to about 1 mm.

In one embodiment, it may be desirable to use piezoelectric ceramics such as Navy Type II materials and related ceramics (e.g., lead zirconium titanate piezoelectric), although other materials having similar properties and composition arelikewise contemplated and may be used. For purposes of constructing the ceramic body 106 (and the piezoelectric element 104 in general), in one example a brick of Navy Type II material can be diced into plates having a thickness on the order of 0.6 mm. These plates can be finished by way of finish grinding operations so that the thickness of the resulting plates is about 0.2 mm. Linear grinding, lapping, and back grinding are all acceptable finish grinding operations. The plates can thereafter be cutinto strips with a width of about 9 mm and the electrodes can be formed, poled, and tested. Plating operations such as sputtering can be used to deposit the gold (Au) plating and the finished plates can be diced to form the individual piezoelectricelements (e.g., the piezoelectric element 104). In one example, a single brick of Navy Type II material can yield approximately 2880 of the piezoelectric element 104. It will be appreciated that the electrodes 122 can be formed using certaindeposition, etching, sputtering, and related processing techniques and processes recognized within the scope and spirit of the present disclosure.

The layers (e.g., the first layer 116 and the second layer 118) of the flexible circuit material 114 can comprise materials such as a polyamide-based film, as well as other materials and films that comprise one or more of polyester (PET),polyimide (PI), polyethylene napthalate (PEN), and polyetherimide (PEI). The layers can be constructed together to form a laminate that is compatible with the processing conditions, operating temperatures, and physical characteristics (e.g., the profileheight P) discussed herein. Conductors such as electrical conductors like metal foil may be included among the layers, or in other examples the conductors can be incorporated amongst the layers such as by using electroplating and related plating anddeposition techniques. These conductors can extend to the electrodes 122 as well as to peripheral edges and areas of the substrate 102. This configuration is useful to conduct the pulse and electrical signals to and from the piezoelectric element 104,an example of which was discussed above in connection with the common substrate (e.g., the common substrate 26 of FIG. 1).

Referring next to FIGS. 4-9, there is provided exemplary embodiments of a piezoelectric sensing device 200 (FIGS. 4 and 5), 300 (FIGS. 6 and 7), and 600 (FIGS. 8 and 9). For purposes of the discussion that follows below, like numerals are usedto identify like components as between FIGS. 2-9, except that the numerals are increased by a multiple of 100 (e.g., 200 in FIGS. 4 and 5, 300 in FIGS. 6 and 7, 600 in FIGS. 8 and 9). The piezoelectric sensing devices 200, 300, and 600 are useful forimplementation in one or more of the configurations of the transducer array 12 discussed in connection with FIG. 1 above.

The piezoelectric sensing device 200 that is depicted in FIGS. 4 and 5, for example, is suited for use in connection with the configuration of the transducer array 12 (FIG. 1) wherein each of the sensing elements 18 is arranged as individualunits. In one embodiment, the piezoelectric sensing device 200 can comprise a substrate 202 and a piezoelectric element 204. The substrate 202 can comprise a flexible circuit material 214 with a receiving area 220 in which is positioned thepiezoelectric element 204. The receiving area 220 can have electrodes 222 including a ground electrode 224 and a hot electrode 226. A solder layer 236 can be disposed on one or more of the electrodes 222 using screen printing techniques recognized inthe art.

The flexible circuit material 214 can comprise a frontside 240 and a backside 242 on which are located the electrodes 222. The piezoelectric sensing device 200 can also comprise one or more cable connections 244 with cable connection pads 246and strain reliefs 248. The cable connection pads 246 can include a ground pad 250 and a hot pad 252, each being coupled to, respectively, the ground electrode 224 and the hot electrode 226 by way of one or more vias 254. The vias 254 extend throughthe flexible circuit material 214, thereby coupling the cable connection pads 246 on the frontside 240 to the electrodes 222 on the backside 242. In one example, a ground plane 256 is also incorporated into the flexible circuit material 214. The groundplane 256 is coupled to the ground electrode 224 and the ground pad 250.

The piezoelectric sensing device 300, as depicted in FIGS. 6 and 7, can be implemented when the transducer array 12 (FIG. 1) utilizes a common substrate (e.g., the common substrate 26 (FIG. 1)). In one embodiment, the piezoelectric sensingdevice 300 can comprise a substrate 302 and a piezoelectric element 304. The substrate 302 can comprise a flexible circuit material 314 with one or more receiving areas 320 configured for receiving the piezoelectric element 304 thereon. The receivingareas 320 can have electrodes 322 including a ground electrode 324 and a hot electrode 326. A solder layer 336 is also included for securing the piezoelectric element 304 to the electrodes 322.

The piezoelectric sensing device 300 can comprise a common substrate 358 in which a plurality of conductors 360 are incorporated. The conductors 360 can include hot conductors 362 and ground conductors 364, each being illustrated as extendingfrom a free end 366 of the common substrate 358. Disposed on the free end 366 is a connector 368 such as a multi-pin connector that is coupled to each of the conductors 360. The connector 368 is likewise configured to couple to a mating connector (notshown) as might be associated with the instrumentation (e.g., instrumentation 14 (FIG. 1)) contemplated herein.

The piezoelectric sensing device 600, as depicted in FIGS. 8 and 9, can also be implemented when the transducer array 12 (FIG. 1) utilizes a common substrate (e.g., the common substrate 26 (FIG. 1)). The piezoelectric sensing device 600 canhave a first side (or backside) 642 and a second side (or front side) 640. In one embodiment, the piezoelectric sensing device 600 can comprise a substrate 602 and a plurality of piezoelectric elements 604 mounted on the backside 642 of the substrate602. The piezoelectric elements 604 can be ceramic piezoelectric transducers (PZT). The substrate 602 can comprise a flexible circuit 660 with a plurality of receiving areas 606 on the backside 642 configured for mounting the piezoelectric elements 604thereon.

The flexible circuit 660 can comprise a plurality of conductors 690. The conductors 690 can include hot conductors 632 and ground conductors 612, 622, 632 extending from a free or first end 696 of the flexible circuit 660. Disposed on the freeend 696 can be a connector 698 such as a multi-pin connector that is coupled to each of the conductors 690. The connector 698 is likewise configured to couple to a mating connector (not shown) as might be associated with the instrumentation (e.g.,instrumentation 14 (FIG. 1)) contemplated herein.

The flexible circuit 660 of the piezoelectric sensing device 600 can comprise a plurality of different layers. In one embodiment illustrated in FIG. 9, the flexible circuit 660 has a double-sided copper-cladded core 610, including a purepolyimide C-stage core 620 between a first copper layer on the back side 642 and a second copper layer on the front side 640. As a C-stage material, the core 620 is fully cured and is therefore relatively insoluble and infusible. In one embodiment, thecore 620 can be 0.005 in. (0.127 mm) thick. The copper layers of the double-sided copper-cladded core 610 can be etched with, e.g., chemicals, to form a plurality of conductors 612, 622, 632 on the front side 640 and the backside 642 of the purepolyimide C-stage core 620. In one embodiment, the copper layers 640, 642 can be 0.0007 in. (0.0178 mm) thick. As shown in FIG. 9, the etching can provide an isolation gap 650 between the backside ground conductors 612 and the backside hot conductors632. A plurality of plated vias 630 extending through the pure polyimide C-stage core 620 can be used to connect the backside ground conductors 612 and the front side ground conductors 622.

In one embodiment of the piezoelectric sensing device 600 illustrated in FIG. 9, the flexible circuit 660 has glass reinforced polyimide C-stage cover layers 616, 626 formed over the conductors 612, 622, 632. In one embodiment, the glassreinforcement can be woven fibreglass with a 1080 glass type. Before processing (e.g., laminating), as a B-stage prepreg material (e.g., low flow polyimide 1080 prepreg), the backside cover layer 616 and the front side cover layer 626 are partiallycured and such that they are not completely fused or dissolved, but rather soften when heated and swell in contact with certain liquids. After processing, the cover layers 616, 626 are fully cured to a C-stage material. Windows 608 can be formed in thebackside cover layer 616 to form the receiving areas 606 configured for receiving the piezoelectric elements 604 thereon and to expose a ground electrode 618 and a hot electrode 638 in each window. A first solder layer 603 secures the piezoelectricelement 604 to the ground electrode 618 and a second solder layer 605 secures the piezoelectric element 604 to the hot electrode 638. Given the material properties of the glass reinforced polyimide C-stage cover layers 616, 626, a laser or other cuttingtechnique may be used to form the windows 608 if etching cannot be used to remove the glass reinforced polyimide C-stage material.

To facilitate soldering, the conductors 612, 622, 632 can be plated with plating layers 614, 624. In one embodiment, the plating can be 0.0005 in. (0.0127 mm) thick. In one embodiment, electrolysis nickel over immersion gold (ENIG) is used toplate the conductors 612, 622, 632 before the cover layers 616, 626 are formed over the conductors 612, 622, 632. In another embodiment, ENIG is used to plate the conductors 612, 622, 632 with the plating layers only after the cover layers 616, 626 areformed over the conductors 612, 622, 632 and the windows 606 are formed to expose the conductors 612, 622, 632 for plating.

The pure polyimide C-stage core 620 and the glass reinforced polyimide C-stage cover layers 616, 626 provide the flexibility and support necessary for the flexible circuit 660 to be installed on curved surfaces of a conduit or othercircumferential devices. The use of a pure polyimide C-stage core 620 and glass reinforced polyimide C-stage cover layers 616, 626 also eliminates impurities or other additives that may decrease the temperature rating of the piezoelectric sensing device600 and allow the piezoelectric sensing device 600 to operate in environments and on devices that are routinely operating well above 120.degree. C. (e.g., nuclear power generation environments).

In one embodiment, the glass reinforced polyimide C-stage cover layers 616, 626 can be formed over the conductors 612, 622, 632 by providing glass-reinforced polyimide B-stage sheets on the front side 640 and the backside 642 of the purepolyimide C-stage core 620, which can also be provided in a sheet, and compressing the polyimide layers between two presses while exposing the layers to temperatures that will form the flexible circuit 660 after lamination. The use of the describedpolyimide layers can avoid the need for using epoxies or other adhesive materials that may have lower temperature ratings than the glass reinforced polyimide cover layers 616, 626 and the pure polyimide C-stage core 620.

Discussing now the implementation of piezoelectric sensing devices such as the piezoelectric sensing devices 100, 200, 300, and 600 discussed above, reference is now directed to FIGS. 10 and 11. FIGS. 10 and 11 illustrate, respectivelyexemplary embodiments of a piezoelectric sensing device 400 and 500, these embodiments being configured for use in measurement systems such as the measurement systems described above and in more detail below. Like numerals are also used to identify likecomponents as between the FIGS. 2-11. However, although some of the features and concepts of the piezoelectric sensing devices of the present disclosure may not be depicted or discussed in connection with FIGS. 10 and 11, it is contemplated that suchfeatures and concepts are applicable to the piezoelectric sensing devices 400 and 500 as well as embodiments and derivation thereof.

There is depicted in FIG. 10, for example, a plurality of piezoelectric sensing devices 400, each of which can comprise a substrate 402 and a piezoelectric element 404. The substrate 402 can include a flexible circuit material 414 with a groundelectrode 424, a hot electrode 426, and a solder layer 436 that is used to secure the piezoelectric element 404 to the substrate 402. The flexible circuit material 414 includes a frontside 440 and a backside 442. In one embodiment, the piezoelectricsensing devices 400 are implemented as part of a measurement system 470, which can comprise a transducer array 472, instrumentation 474, and a connection 476 such as one or more cables 478 that are coupled to the piezoelectric element 404. Themeasurement system 470 can also comprise a connection terminal 480 to aggregate the cables 478, acting in one example as a central hub for communicating signals to and from the instrumentation 474 and the piezoelectric sensing devices 400 of thetransducer array 472.

In one embodiment, the piezoelectric sensing devices 400 are secured to a surface 482 of a target 484 using a couplant 486 such as an adhesive that is disposed on the backside 442 of the substrate 402. To further ensure proper functioning andcoupling of the piezoelectric sensing devices 400 to the surface 482, one or more outer structures 488 can be utilized such as a protective layer 490 and a fastening mechanism 492. These outer structures 488 can be incorporated as part of thepiezoelectric sensing devices 400 or in one embodiment the outer structures 488 comprise one or more pieces separate from the piezoelectric sensing devices 400. Assembly of the pieces of the outer structures 488 can occur at the time of implementationand installation of piezoelectric sensing devices 400 and the measurement system 470 generally.

The couplant 486 can be disposed on surfaces of the substrate 402, as depicted in FIG. 10, as well as on the piezoelectric element 404. Care should be taken during application to avoid degradation of the performance of the piezoelectric element404. In addition to performance characteristics, it may be desirable that materials for use as the couplant 486 are compatible with the material characteristics of the substrate 402 and the target 484. In one example, adhesives such as acrylicadhesives can be applied at as a layer with a nominal initial thickness of about 1 mm. Other adhesives and related materials that may be likewise acceptable include, but are not limited to, cyanocrylates, epoxies, solvent-based adhesives, and cold-flowadhesives, as well as combinations and derivations thereof.

The protective layer 490 is used to prevent damage to the underlying structure, e.g., the piezoelectric sensing devices 400. Materials can likewise have electrically insulating properties thus providing protection from the outer environment aswell as preventing arcing, shorting, and other electrical-induced failures that can occur. Exemplary materials for use as the protective layer 490 can include silicon, nylon, neoprene, polymeric materials, and combinations and derivations thereof.

The fastening mechanism 492 can be in the form of the band-like structure illustrated in FIG. 11. When the target 484 is a conduit or other circumferential device, such structures can be affixed about the circumference. These structures canincorporate secondary fastening and tightening features that reduce the diameter of the band about the conduit, thereby applying a force onto the piezoelectric sensing devices 400. For other configurations of the target 484, such as for targets withflat or irregular constructions, the fastening mechanism 492 may be configured with devices that are designed for the specific configuration of the target 484. These devices may include magnets and magnetized implements that can cause to be applied toforce onto the piezoelectric sensing devices 400.

Referring now to FIG. 11, it is seen that the piezoelectric sensing device 500 can comprise a substrate 502 and a piezoelectric element 504. The substrate 502 can comprise a ground electrode 524 and a hot electrode 526, and a solder layer 536is included as contemplated herein. The substrate 502 is arranged as a common substrate 558 with a free end 566 on which is disposed a connector 568. The piezoelectric sensing device 500 is part of a measurement system 570, which can comprise atransducer array 572, instrumentation 574, and a connection 576 coupled therebetween. To secure the piezoelectric sensing device 500, a couplant 586 is used and further protection is afforded by a protective layer 590 and a fastening mechanism 592. Inone embodiment, the connection 576 can comprise a single cable 594 that is coupled to the connector 568 and to the instrumentation 574. The single cable 594 can comprise, for example, a mating connector 596 that is configured to mate with the connector568.

This written description uses examples to disclose embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.